The present invention relates to onboard tire inflation systems for automatically maintaining the inflation pressure of the pneumatic tires on both non-powered and powered axles of moving vehicles such as tractor trailers and tractors.
Onboard automatic tire inflation systems are currently available for use on trucks and other vehicles. Such systems have been successfully used in non-powered vehicle axle assemblies such as on tractor trailers (see, e.g., U.S. Pat. Nos. 6,105,645 and 7,418,989) and more recently on powered axle assemblies (see, e.g., U.S. Pat. No. 7,896,045). Such systems deliver make-up air to a vehicle tire in the event that the tire is punctured or begins to lose air for other reasons. The disclosures of the above identified patents are incorporated herein by reference.
By way of example, an onboard system for maintaining a predetermined pressure in each of the tires of a non-powered truck tandem axle assembly is currently available from Airgo, Inc. of Edmond, Okla. The Airgo unit includes a tire inflation system which delivers compressed air from an onboard compressor (e.g., the compressor used for supplying air to the truck brakes) to the tires through the interior of the tandem axle, or a tube extending through the axle, in the event that a leak occurs in any of the four tandem axle tires. The Airgo unit also includes: a pair of rotary seals provided proximate the outer ends of the non-powered tandem axle; a set of air lines extending from the rotary seals for delivering air from the interior of the axle, through the rotary seals, to each of the four tires; check valves provided in the air lines for preventing reverse air flow from the tires to the axle; and an indicator light which alerts the operator that a leak has developed. The system controls the make-up air flow in accordance with the operating pressure required by the tires. For most tandem truck axles, the automatic inflation system will typically be operable for providing a sufficient make-up air flow to maintain a tire pressure of at least 90 psig and more preferably at least 95 psig. Automatic tire inflation systems of this type are described in U.S. Pat. Nos. 6,105,645 and 7,418,989 identified above.
Automatic tire inflation systems are susceptible to failures, however, which may result in deflation of one or more of the tires served by the system. A failure of a pressure regulator utilized in the system or of a valve or air conduit between the regulator to the tires can result in a loss of air at the failure and through the pneumatic conveyance. The installation of a check valve at the tire would prevent flow from the tire in the event of such a failure, while allowing the tire to be inflated as necessary. Such a valve, however, would prevent the tire from being deflated when necessary and the ability to deflate a tire in automatic tire inflation systems is a desirable feature. Tires may be inflated to the proper pressure when cold, but warming of the tire after inflation can result in pressures that are too high. A similar effect occurs when the vehicle undergoes changes in altitude. Tires inflated to proper pressures at low altitude result in excessive tire pressures when a vehicle travels to a high altitude. Deflation of tires to the proper inflation level prevents the operation of the tires in an over-inflated condition and may be useful in balancing loads or adjusting to wind or, if off road, adjusting to soil conditions.
Therefore, it would be highly desirable to be able to develop an automatic tire inflation system that would prevent the tires from being fully deflated in the event of a system failure while allowing for regulated tire deflation to maintain the tires at their proper operating pressure. Such a system is provided by the present invention.